you don't even need all of that to track people.

there was a bit of a kerfuffle where a dataset that literally only contained the start, end and time, and some deanonymized data of NYC taxi rides was successfully deanonymized and used to track celebrities. Most people have fairly sparse, unique travel patterns, and so armed with only a few known paparazzi photos you could accurately derive their whole travel history. https://www.fastcompany.com/3036573/nyc-taxi-data-blunder-re...

Yes, but as I said it is possible to use a separate ID for entry and exit, so unless they were willing to perform a CCTV trawl then your entire journey could not be assessed. The penalty for this kind of anonymity is paying top fare for entry and exit, so only a very rich tube user could bear the cost. The thing that got people to use Oyster in the first place was 'discounted' prices, as in they bumped the price for a paper ticket when Oyster cards were introduced and kept the old prices for Oyster only journeys. Make of that what you will. Paper tickets are still available as of 2026 last time I checked.

There was a similar data trawl when Boris bikes were introduced, and some of the information gleaned from that was quite hilarious but I can't find a link because it was from the old world and now lost in enshitted search.